DC short-circuit faults pose a hazard to the operation of a modular multilevel converter (MMC)-based high voltage direct current (HVDC) system

necessitating reliable fault clearing solutions with rapid reaction. However

because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system

strong electromagnetic oscillations with multiple frequencies occur during clearance transients. These oscillations will disturb the HVDC system's protection and control systems. Therefore

this paper focuses on the modeling of these oscillations. First

an equivalent circuit for the MMC-based HVDC system is proposed

taking into account the parasitic capacitances of the system's major components

such as DC reactors

connecting cables

and DC circuit breakers (DCCBs). Second

four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs

and the associated analytical equations for the oscillation frequencies are derived. Third

a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole (PTP) short-circuit test. Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz. The measured waveforms correspond well with simulated results

including the parasitic characteristics. Additionally

the relative errors between the simulated and measured frequencies are less than 5%.